Continuous recording of thickness, using a measuring roller with a bath-shaped guide shoe, articulated in parallel (long timber)

ABSTRACT

The invention relates to a measuring device, which allows the thickness ( 4 ) of an elongated, panel-type workpiece, lying on a reference plane ( 2 ) and travelling in the direction of the arrow ( 3 ), to be continuously recorded. Said measuring device is provided with a guide shoe ( 16 ), which is bath-shaped and open at the top and is pivotally mounted in a machine frame ( 7 ) on parallelogram-shaped steering elements ( 22 ). A measuring roller ( 9 ), which projects slightly out of a cavity in a base section ( 19 ) that always runs parallel to the reference plane ( 2 ), is located inside the guide shoe ( 16 ). Said roller is supported in the interior of the guide shoe by rollers ( 34 ) on both sides of the recess. The measuring roller ( 9 ) is in contact with the reference plane ( 2 ) and after a deflection of the guide shoe ( 16 ), comes into contact with the measuring surface of the workpiece, a measured value that represents the thickness ( 4 ) being derived from said deflection. Compared with devices in prior art, a substantially smaller vertical acceleration takes place as a result of the special mounting of the guide shoe ( 16 ) by means of the parallel steering elements ( 22 ), thus facilitating higher advance speeds of the workpiece, without causing excessive material stress.

[0001] The invention relates to a measuring device according to the preamble of claim 1.

[0002] In order to check the thickness of elongate measurement objects, e.g. long timbers or panel-shaped material to be measured, it is known to provide a measuring system which is characterised by at least one measuring roller which is held above the measurement object and can be moved in the direction towards same. The zero setting of the measuring roller which is operatively connected to a pneumatic drive is formed by means of a reference plane, on which lies the measurement object and along which said measurement object can be moved at a defined speed. For its part, the measuring roller is also operatively connected to a measuring transducer, by means of which the displacement path of said measuring roller can be represented by a corresponding electrical signal.

[0003] The measuring procedure in the case of this known measuring system is performed in such a manner that the measuring roller is moved out from its withdrawn position above the measurement object in the direction of said object and brought into contact therewith, after the moving measurement object has arrived at a position below the measuring roller. However, in dependence upon the advance speeds of the measurement object on the one hand and the measuring roller on the other hand, it is not possible as a result to record the thickness of a starting region of the measurement object. Furthermore, the measuring roller is withdrawn starting from its position rolling on the surface of the measurement object, before the end of the measurement object is reached. This limitation at the beginning and the end of the measuring path on the measurement object was adapted inter alia to avoid causing any mechanical damage to the measuring system.

[0004] In order to improve the manner in which the measuring systems are protected from mechanical destruction measuring devices are currently used, in which a run-in ramp is provided. For this purpose, a run-in ramp is provided which is mounted on its end so as to be able to pivot about a [lacuna] in parallel with a reference plane. This run-in ramp is operatively connected at its free end facing away from its articulation to a measuring roller which by means of running rollers on both sides is supported on the inner side of this ramp and passes slightly through the base region thereof. By reason of the measurement object which abuts against the underside of the base region of the run-in ramp, said run-in ramp is pivoted, wherein during the course of further advance movement the measuring roller finally moves into position against the surface of the measurement object. In dependence upon the advance speed and also upon the comparatively long lever arm between, on the one hand, the articulation point of the run-in ramp and, on the other hand, the measuring roller, extraordinarily high acceleration moments are produced for the measuring roller and above all the elements of the measuring systems which are functionally downstream of the measuring roller. In order to avoid vibration problems which arise due to an acceleration of the run-in ramp, there is provided a control, which is allocated to the pneumatic drive of the measuring roller, with the proviso that a counter force is developed at an early stage which suppresses excessive vibration. However, the disadvantage in this case is that the acceleration moments which are to be compensated are dependent both upon the advance movement of the measurement object and also upon its thickness.

[0005] The purpose of this known measuring system is to obtain the most complete information possible on the thickness of the measurement objects—as seen in the longitudinal direction thereof—wherein the measurement objects are guided through the measuring system at a defined advance speed and at different mutual end-side spaced intervals. One essential feature of these known measuring systems is that each time a measurement object has been passed through by means of the said pneumatic drive, the measuring roller is moved either to a withdrawn position or to a zero setting. The periods of time available for these considerable deflection movements turn out to be comparatively short in dependence upon the advance speed of the measurement objects and the mutual spaced intervals between them and consequently these periods must be concluded at a correspondingly high speed and with rapid reverse-control procedures. In addition to high material stress, this can also lead to considerable noise development. As a result, these conditions restrict the advance speed of the measurement objects.

[0006] Against this background, it is the object of the invention to design a measuring device of the type stated in the introduction with the proviso that the mechanical stress of the actual measuring system, in particular that of the measuring roller and the function elements disposed downstream thereof is reduced and in relation to the prior art set forth in the introduction it is possible to achieve an increase in the speed at which the measurement objects are advanced. In the case of this type of measuring device, this object is achieved by virtue of the features of the characterising part of claim 1.

[0007] Accordingly, an essential aspect of the invention is a guide shoe which comprises a base section which extends in parallel with the reference plane and said guide shoe is pivotally disposed with respect to the machine frame by way of parallelogram-shaped levers. The end points of the parallelogram-shaped levers which form the articulation points thereof lie on the corners of a parallelogram, so that the parallelism between the base section and the reference plane is also maintained during the pivot movement of the guide shoe.

[0008] Supported on the guide shoe, lying opposite the reference plane, is the measuring head, of which the measuring roller passes slightly through a recess in the said base section. The measuring roller is intended to roll on the measurement object in a manner which is known per se.

[0009] As such the guide shoe is intended to be deflected, in particular pivoted, by an abutting measurement object, wherein the vertical component of the pivot movement is used in order to displace the measuring head.

[0010] As a result of the articulation of the guide shoe in the manner of parallel steering elements and of which the parallelogram-shaped levers extend virtually perpendicularly in a starting position or in such a manner that the respective lower articulation points are slightly deflected in the direction in which the measurement object is advanced, the abutment of the measurement object against the facing base region of the guide shoe causes said guide shoe to perform a movement which is made up of “simultaneous movement” in the advance direction and a vertical movement. The movement referred to lastly is linked via a sine function to the pivoting movement of the parallelogram-shaped levers, in particular their pivot angle about their upper articulation points, so as to produce in comparison with the prior art an extraordinarily small initial vertical acceleration and therefore loading of the measuring roller or the elements functionally downstream thereof.

[0011] Corresponding to the [lacuna] by the length of the parallelogram-shaped levers and the geometric formation of the guide shoe base region facing the measurement object, the measuring system, in relation to the prior art set forth in the introduction, is subjected to substantially lower acceleration at the same advance speed, wherein the thickness of the complete length of the measurement object is measured. In turn, these acceleration conditions allow comparatively higher advance speeds, without the problem of excessive material stress arising.

[0012] The features of claims 2 and 3 are directed to the mounting of the measuring system on the guide shoe and to the displaceability thereof. Since the measuring system can only be moved vertically, it is necessary to provide a movable support on the guide shoe in parallel with the reference plane.

[0013] The features of claims 4 and 5 are directed to the further embodiment of the system of parallelogram-shaped levers of the measuring head and of the guide shoe. It is essential that the guide shoe is held under resilient force in position against the running rollers. This resilient force in conjunction with the counter force applied by way of the drive of the measuring system serves to produce the measuring force which determines the contact pressure of the measuring roller on the measurement object.

[0014] The features of claim 6 are directed to the embodiment of the base region of the guide shoe which is intended to cooperate directly inter alia with the edges or the surface of the measurement object to be treated and its geometric shape in conjunction with the parallel-articulation of the guide shoe on the machine frame serves to influence significantly the movement and in particular the acceleration conditions of the measuring system.

[0015] The features of claims 7 and 8 are directed to the cooperation of the control device and the drive of the measuring system. Basically, the movements of the measuring system should be kept as small as possible and this is demonstrated initially by virtue of the fact that the measuring system is held between two consecutive measurement objects by means of its drive, e.g. a pneumatic drive, in a particular displacement position corresponding to the measured value of thickness of the respectively preceding measurement object. Equally, there is no complete withdrawal movement or a movement to a zero setting. The control device is set up in conjunction with peripheral elements associated therewith such that the drive of the measuring system in this sense is then controlled if the gap between two measurement objects is greater than a distance determined by the longitudinal extension of the guide shoe. If, conversely, the gap between two measurement objects is shorter than this distance, a corresponding reverse-control of the drive of the measuring system is omitted. This basic actual value storage of a measured value of thickness of a preceding measurement object produces a substantially lower level of mechanical stress on the measuring system, lower noise development and a lower energy requirement for the drive of the measuring system, i.e. lower air consumption in the case of a pneumatic drive.

[0016] It is also possible to reset the measuring head in a very short time by reason of the short displacement path.

[0017] The features of claims 9 and 10 are directed to those embodiments of the measuring device in accordance with the invention, in which the measurement object—as seen in the direction of its longitudinal extension—is scanned on the upperside and underside using a measuring roller, wherein a measured value of thickness of the measurement object is derived from the displacement of the two measuring rollers with respect to a reference plane, so that in general the difference in the displacement of the two measuring rollers is measured. Preferably, it will be assumed that in comparison with the upper measuring roller, the lower measuring roller is only displaced slightly with respect to the reference plane, so that the lower measuring roller is operated without a guide shoe. However, it is also possible to operate the lower measuring roller with a guide shoe which structurally can correspond to the upper guide shoe, wherein by means of a corresponding actuation of the drive allocated to the lower guide shoe or to the lower measuring system, it is necessary to ensure that the guide shoe or the measuring roller lies in position against the underside of the measurement object.

[0018] The features of claim 11 are directed towards increasing the operational security of the measuring device, in particular to protecting the measuring system in the event of a malfunction in the energy supply to the drive.

[0019] The invention will be explained in detail hereinunder with reference to the exemplified embodiment illustrated schematically in the drawings, in which:

[0020]FIG. 1 shows a side view of a measuring device to be ascribed to the prior art in a partial sectional illustration;

[0021]FIG. 2 shows a side view of the measuring device according to the invention in a partial sectional illustration;

[0022]FIG. 3 shows a side view of the guide shoe used within the framework of the measuring device according to a sectional plane III-III in FIG. 3;

[0023]FIG. 4 shows a plan view of the said guide shoe according to the arrow IV in FIG. 3.

[0024] In FIG. 1, the reference numeral 1 designates a panel-type measurement object which lies on a reference plane 2 and is moved at a defined speed in the direction of the arrow 3. The measurement object 1 comprises a finite thickness 4 perpendicular to the said reference plane 2, of which the progression—as seen in the longitudinal direction of the measurement object 1—is to be recorded during the passage of the said measurement object through the measuring device 5. The longitudinal extension of the measurement object 1 in this case runs parallel with the reference plane 2.

[0025] The reference numeral 6 designates a run-in ramp which is formed as an elongate bath-shaped basic body which is open on the upperside and which is articulated at its one end in a bearing block 8, which is affixed to a machine frame 7, so as to be able to pivot about a horizontal axis extending perpendicularly to the advance direction 3. The bearing block 8 is located at a spaced interval above the reference plane 2.

[0026] The reference numeral 9 designates a measuring roller which in the illustration shown lies on the reference plane 2 and in this case passes through a recess [not illustrated in the drawing] of the base region 10 of the run-in ramp 6. The measuring roller 9 is mounted at the end of a measuring linkage 11 in such a manner as to be able to rotate about an axis extending in parallel with the reference plane 2 and perpendicularly to the advance direction 3, wherein the entire system consisting of the measuring roller 9 and the measuring linkage 11 forms a measuring system which is operatively connected to a measuring transducer which is also not illustrated in the drawing. Its functional principle is to convert vertical movements of the measuring roller 9 with respect to the reference plane 2, i.e. in the direction of the arrows 12, into an electrical signal. This signal is transmitted to a control device and further processed in a suitable manner, in particular it is illustrated visually, stored etc.

[0027] The said measuring system is vertically supported on the inner side of the base region 10 by means of freely rolling running rollers 13 which are mounted on the measuring linkage 11 with the proviso that the measuring roller 9 protrudes by a defined distance from the underside of the run-in ramp 6.

[0028] Also not illustrated in the drawing is a drive, e.g. a pneumatic drive which is connected to the said control device and by means of which the measuring system can be displaced in the direction of the arrows 12.

[0029] The principle of this known measuring device is that by reason of the measurement object 1 which is moved at a defined speed in the advance direction 3 and which abuts with its edge 14 against the base region 10 of the run-in ramp 6, the said run-in ramp is pivoted about the axis of the bearing block 8, wherein this pivot movement triggers a vertical movement of the measuring linkage 11 by way of the said running rollers 13. This pivot movement ultimately causes the measuring roller 9 to roll on the upper side 15 of the measurement object, wherein according to the vertical deflection of the measuring system via the measuring transducer a corresponding measured value is generated. In each case, the aim is to record the progression of the thickness 4 of the measurement object in the direction of its longitudinal extension.

[0030] However, in dependence upon the thickness 4 of the measurement object 1 and the spaced intervals between the articulation point 8′ of the run-in ramp 6 on the one hand and the primary abutment point of the measuring point 1 against the said base region 10 or the running rollers 13 on the other hand, considerable vertical acceleration of the measuring system is achieved. In particular, the relationship of the spacing of the running rollers from the articulation point to the spacing of the said abutment point from the articulation point serves accordingly to enhance the deflection movement of the run-in ramp 6 at the point where it interacts with the running rollers 13 and therefore the measuring system.

[0031] In order to avoid vibration problem and also to protect the measuring system mechanically, these kinematic boundary conditions render it necessary to develop a counter force by way of the drive allocated to said system, in coordination with the deflection movement of the run-in ramp 6. On the whole, these characteristics particularly in the case of measurement objects having comparatively large thickness dimensions inevitably serve, however, to limit the advance speed of the measurement object 1 considerably.

[0032] In the embodiment of a measuring device according to the invention illustrated by way of example in FIGS. 2 to 4 and explained in detail hereinunder, functional elements which correspond to those in FIG. 1 are numbered accordingly.

[0033] The reference numeral 16 designates a guide shoe which is mounted in a manner to be explained in detail hereinunder so as to be able to swing on the machine frame 7 and comprises a base section which is intended and arranged to cooperate with the measurement object 1. Seen from left to right, the base section consists of the series arrangement of a first comparatively steep ramp section 17, which extends e.g. at an angle of 45° with respect to the reference plane 2, a ramp section 18 adjoining said first ramp section and extending at a substantially shallower angle with respect to the reference plane 2, an adjoining base section 19 extending in parallel with the reference plane, a ramp section 20 which adjoins the last named base section and ascends with respect to the reference plane 2 in turn at a comparatively shallow angle, and an adjoining ramp section 21 extending at a comparatively steeper angle with respect to the reference plane 2. Adjoining the said ramp sections 17 to 20 is a sidewall 21′, so that the guide shoe 16 generally has a bath-shaped configuration which is open towards the upper side.

[0034] The reference numeral 22 designates two identically configured parallelogram-shaped levers which are in particular the same length and which are articulated in a pivotal manner on the horizontally mutually spaced points 23, 24 of the machine frame 7. The points 23, 24 can each be formed by bolts which are located in a common horizontal plane.

[0035] Perpendicular to the plane of the drawing in FIG. 2, the parallelogram-shaped levers 22 are disposed in each case in pairs at a spaced interval with respect to each other, wherein their respective lower ends, i.e. the end remote from the points 23, 24, are articulated in a pivotal manner in points 25, 26 of the sidewalls 21′ of the guide shoe 16, which points 25, 26 are located in turn in a common horizontal plane. In the starting position of the guide shoe 16 shown in FIG. 1, the two parallelogram-shaped levers 22 extend at an acute angle with respect to vertical planes extending through the points 23, 24, and furthermore such that the lower points 25, 26 are offset in the direction of the arrow 3 with respect to the upper points 23, 24. It is evident in these embodiments that the arrangement of the parallelogram-shaped levers forms a parallel steering arrangement for the guide shoe 16. It is essential that, with respect to the plane of the drawing in FIG. 1, on the one hand the points 23, 24 and on the other hand the points 25, 26 lie in each case on mutually parallel straight lines which also extend in parallel with the base section 19.

[0036] The reference numeral 27 designates a draw spring, of which one end is articulated on a point 28 located at a small spacing from the point 23 on the end of the parallelogram-shaped lever 22 facing said point, and the other end of said draw spring is articulated to a point 29 on the sidewall 2 of the guide shoe 16 which is spaced apart from the point 25 at this site. Each of the two parallelogram-shaped levers 22 which are adjacent to each other perpendicular to the plane of the drawing in FIG. 1 are allocated such a draw spring 27. It is evident that under the influence of the draw springs 27, the guide shoe 66 is drawn under spring bias towards the measuring system to be described hereinunder.

[0037] The reference numeral 9 designates a measuring roller which in the illustration shown in FIG. 2 lies on the reference plane 2 and in this case passes through a recess 30 in the base section 19 of the guide shoe 16. The measuring roller 9 is mounted on a roller holder 31 in such a manner as to be able to rotate about an axis 32 extending in parallel with the reference plane 2. The roller holder 31 is connected to a vertically mounted measuring linkage 33 which is operatively connected to a measuring transducer [not illustrated in the drawing]. The principle of said measuring transducer is based upon the fact that vertical movements of the measuring roller 9 with respect to the reference plane 2, i.e. in the direction of the arrows 12, are converted into an electrical signal, preferably a digital signal. This signal is transmitted to a control device and visually displayed, stored etc. therein in a suitable manner.

[0038] As illustrated in FIG. 4, the measuring roller 9 is located according to the positioning of the recess 30 in a central region of the base section 19, wherein on both sides of the roller holder 31, running rollers 34 are each mounted in such a manner as to be able to rotate about axes 35 in parallel with the axis 32 but below same. Both axes 32, 35 extend horizontally and perpendicularly with respect to the arrow 3, wherein the two running rollers 34 are disposed laterally in relation to the measuring roller 9 and therefore in the regions 36 on both sides of the recess 30 are mounted in such a manner as to be able to roll on the base section 19 of the guide shoe 16. The axes 32, 35 are positioned in conjunction with the diameters of the measuring roller 9 on the one hand and the running rollers 34 on the other hand with the proviso that—as shown in FIG. 2 of the drawing—the measuring roller 29 protrudes slightly out of the underside of the guide shoe 16.

[0039] The measuring linkage 33 is also operatively connected to a drive [not illustrated in the drawing], e.g. a pneumatically actuated piston-cylinder unit by means of which the running rollers 34 are held in position against the guide shoe 16 in the regions 36 and in conjunction with the draw springs 27 the required measuring force is applied.

[0040] The statements above show that the functional principle of the measuring device in accordance with the invention is based upon the fact that the guide shoe 16 can be pivoted by reason of its articulation on the points 23, 24, wherein only the vertical component of the total movement of the guide shoe 16 is transmitted by way of the running rollers 34 to the measuring linkage 33. The measurement object 1 which is moved in the direction of the arrow 3 in parallel with the reference plane 2 abuts with its corner 37 against the steeply extending ramp section 17 of the guide shoe 16, with which the deflection procedure of the guide shoe 16 about the points 23, 24 commences. The continuation of the deflection movement of the guide shoe 16 is determined kinematically by the consecutive ramp sections 17, 18, in particular their absolute lengths and angles with respect to the reference plane 2. Since merely the vertical component of the pivot movement of the guide shoe 16 is transmitted by way of the measuring roller 9, in comparison with the prior art set forth in the introduction a substantially lower vertical acceleration is achieved for the measuring roller 9 including functional elements disposed downstream thereof in the direction of the arrows 12. According to the angles of the consecutive ramp sections 17, 18 and of the base section 19, the pivot movement of the guide shoe 16 is characterised by an initially rapid acceleration which in the region of the ramp section 18 is characterised by a very much lower acceleration, in particular in the vertical direction also.

[0041] Starting from a “zero-setting” of the measuring system, in which the measuring roller 9 records the level of the reference plane 2, the measurement object 1 moving in the direction of the arrow 3 causes the guide shoe 16 and thus the measuring roller 9 to deflect to the actual value of the thickness 4 of the measurement object 1, wherein as a consequence the progression of this thickness value in the longitudinal direction of the measurement object 1 is scanned and logged. During this measuring procedure—as seen in the longitudinal direction of the measurement object 1—the measuring roller 9 is in contact with the side of the measurement object 1 facing it. Upon reaching the end of the measurement object 1, this state of deflection of the measuring roller 9 is stored as the desired value for the value of the thickness 4 of the subsequent measurement object. By way of the drive allocated to the measuring linkage, the running rollers 34 are held constantly in position against the base section 19.

[0042] In the event that the spacing between two consecutive measurement objects 1—as seen in the direction of the arrow 3—is smaller than a distance determined by the longitudinal extension of the guide shoe 16, so that by reason of the fact that the guide shoe 16 lies against the consecutive measurement objects 1, the guide shoe 16 is not able to pivot in any event up to the level of the reference plane 2, this spacing can be bridged without reversing the control of the drive of the measuring linkage 33.

[0043] In contrast, if the said gap turns out to be larger than the distance determined by the longitudinal extension of the guide shoe 16, reversing the control of the drive of the measuring linkage 33 ensures that said linkage remains in the last extended position and in any event is not moved down to the level of the reference plane 2. In actual fact, the measured value of the thickness of a measurement object 1 is stored as a desired value for the next measurement object 1. For this mode of operation it is necessary that the speed and the position of the measurement objects 1 can be established precisely by suitable sensors and that signals describing the status of movement and the position of the measurement objects are available in the higher-ranking control which serves also to control the drive of the measuring head. In each case, any recording of a measured value between two measurement objects is suppressed.

[0044] By reason of the measuring linkage movement which is caused by the configuration of the guide shoe 16 and is performed at a lower acceleration in comparison with the prior art, and also by reason of the opportunity provided by the guide shoes of bridging two consecutive measurement objects or storing the actual value of the thickness of the respectively preceding measurement object, there is also the advantage of substantially lower noise development in addition to a lower wear-inducing operation of the measuring device, reduced energy requirement or consumption of compressed air.

[0045] A measuring device in accordance with the invention has been described in the above presentation such that on one side of a reference plane 2 there is located a measuring system which cooperates with a guide shoe 16. For example, this functional principle can be extended such that below the measurement object to be measured there is located a measuring roller which in the same manner as the measuring roller located above the measurement object forms a part of a measuring system. Measuring the thickness in this case is based upon an evaluation of the deflection of the two measuring rollers, hence upon the formation of a difference value. 

1. Measuring device for continuously recording the thickness (4) of elongate, panel-type measurement objects (1), having at least one measuring system which is accommodated in a machine frame (7), is provided with a measuring roller (9), can be moved in the direction towards and away from a reference plane (2) and which can be moved by way of the measuring roller (9) into position against the reference plane (2) or a measuring surface of the measurement object (1) which is moved in the direction (3) of its longitudinal extension, so that from the distance of the measuring surface from the reference plane (2) it is possible to derive a measured value which represents the thickness (4) of the measurement object (1), having a measuring transducer which is operatively connected to the measuring system and is intended and arranged to generate an electrical signal representing the displacement path of the measuring roller (9), having a drive for the measuring system and a control device which is operatively connected at least to the drive and to the measuring transducer, characterised by at least one guide shoe (16) which is disposed in a pivotable manner on two mutually spaced apart oscillating cranks or parallelogram-shaped levers (22), which are arranged in the manner of parallel steering elements, on the machine frame (7) and which guide shoe comprises at least one base section (19) which extends in parallel with the reference plane (2) and which is provided with a recess (30) accommodating the measuring roller (9) and the said base section is supported on the measuring system with respect to the reference plane (2).
 2. Measuring device as claimed in claim 1, characterised in that the measuring roller (9) is supported in a manner known per se by way of running rollers (34) on both sides of the recess (30) on the base section (19) of the guide shoe (16), wherein the measuring roller (9) protrudes on the underside out of the guide shoe (16) by a defined distance.
 3. Measuring device as claimed in claim 1 or 2, characterised in that the measuring system is able to move in directions (12) perpendicular to the reference plane (2).
 4. Measuring device as claimed in any one of the preceding claims 1 to 3, characterised in that in the non-deflected state of the guide shoe (16), the parallelogram-shaped levers (22) are deflected slightly in the said direction (3) with respect to a plane which is vertical to the reference plane (2).
 5. Measuring device as claimed in any one of the preceding claims 1 to 4, characterised in that the guide shoe (16) is held under resilient force in position against the measuring system.
 6. Measuring device as claimed in any one of the preceding claims 1 to 5, characterised in that the base region of the guide shoe (16)—as seen in the direction (3)—consists of the series arrangement of a comparatively steep ramp section (17), a comparatively flat ramp section (18), the base section (19), a comparatively flat ramp section (20) and a comparatively steep ramp section (21), wherein the two first-named ramp sections (17, 18) are inclined in the direction (3) and the two last-named ramp sections (20, 21) extend in an ascending manner in this direction (3).
 7. Measuring device as claimed in any one of the preceding claims 1 to 6, characterised in that the control device is arranged with the proviso that when the distance between two consecutive measurement objects (1) exceeds a distance determined by the longitudinal extension of the guide shoe (16), a reverse-control of the drive of the measuring system serves to hold the guide shoe (16) at a height position corresponding at least substantially to the thickness (4) of the respectively preceding workpiece (1).
 8. Measuring device as claimed in any one of the preceding claims 1 to 7, characterised in that the control device is arranged with the proviso that when the distance between two consecutive measurement objects (1) is less than a distance determined by the longitudinal extension of the guide shoe (16), the measuring procedure can be continued without reversing the control of the drive of the measuring system, and thus suppressing the recording of measured values in the region between two consecutive measurement objects (1).
 9. Measuring device as claimed in any one of the preceding claims 1 to 8, characterised by a guide shoe (16) which is disposed and articulated above the measurement object (1) and which is connected to one measuring system by way of the measuring roller (9), which is intended to scan the upperside (15) of the measurement object, and by a further measuring roller which is intended to scan the underside of the measurement object (1) and is connected to a further measuring system, wherein from the displacement position of the two measuring rollers with respect to the reference plane (2) it is possible to derive a measured value for the thickness (4) of the measurement object (1).
 10. Measuring device as claimed in any one of the preceding claims 1 to 8, characterised by a first guide shoe (16) which is disposed and articulated above the measurement object (1) and which is connected to one measuring system by way of the measuring roller (9) which is intended to scan the upperside (15) of the measuring object (1), and by a second guide shoe which is disposed and articulated below the measurement object (1) and which is connected to a further measuring system by way of a further measuring roller which is intended to scan the underside of the measurement object (1), wherein from the displacement position of the two measuring rollers with respect to the reference plane (2) it is possible to derive a measured value for the thickness (4) of the measurement object (1).
 11. Measuring device as claimed in any one of claims 1 to 10, characterised in that the control device is connected to the drive(s) of the measuring system(s) and that the control device is arranged in such a manner that in the event of an interruption in the power supply to the drive(s), the measuring system(s) remains/remain in its/their last position(s) or is/are moved to a withdrawn position. 